1. Field of the Invention
This invention pertains generally to printing or typing equipment involving the use of a direct thermal printing process or thermal transfer process to transfer a dry film impression onto an image carrying tape. More particularly, this invention pertains to a novel cassette for carrying the tape.
2. Background of the Invention
In the field of commercial art, there is a significant need for simple means for transferring prefabricated letters or characters to a "paste-up" sheet for later photographing and printing. The earliest technology involving letter transfers was that of dry rub-on transfer sheets which had a series of characters preprinted thereon. These materials, however, are limited by the number of characters available on the sheet and must be very carefully aligned to produce acceptable images. Machines were later developed which printed such letters on a continuous adhesive tape. The first such machines employed print disks having raised characters. Such machines used impact printing to transfer pigment to a carrier tape. Some machines were keyboard driven while others were manual "spin and print" machines. See, for example, U.S. Pat. No. 3,912,064; 4,243,333; 4,462,708 and 4,579,056.
The impact printing machines mentioned above had many advantages over the rub-on letters, but still suffered from certain limitations. Specifically, these machines were necessarily complicated, heavy and relatively slow since the printing effect was accomplished by using physical force against the type face with the print media and pigment ribbon in between. Such machines were also restricted to pigment transfer of some form. In addition, an expensive type disk had to be molded for every point size, type style and language, leading to enormous costs in creating a suitable library. Certain foreign languages which are written either right to left or vertically, would require very specialized type disks. Speed was further limited because the type disks had to physically move to a new location to print each successive character. Finally, the resulting output was generally not considered smear proof and would have to be further coated if used in areas where frequent contact with the print surface was anticipated.
Thermal transfer printing, such as that known in inexpensive portable typewriters (for example Canon Typestar 5.TM., etc.), employed a new technology which used a heat generating print head to melt a wax-pigment from a carrier ribbon to a receiving tape. By using digital technology, characters could be formed of a sequence of pixels and print disks were not required. A related technology is direct thermal printing where an image is created on a thermally sensitive receiving paper directly by the head without the use of an intermediate carrier ribbon.
Thermal transfer has been applied in commercial art printing machines. Such a machine is marketed under the registered trademark Merlin Express.RTM. by Varitronics, Inc., assignee of the present invention. The Merlin Express.RTM. is the subject matter of co-pending and commonly assigned U.S. patent application Ser. Nos. 934,644 (now U.S. Pat. No. 4,815,871) and 934,650 (abandoned and refiled as 289471, which we abandoned and refiled as 584436) filed Nov. 25, 1986 which are continuation-in-part applications of U.S. patent application Ser. Nos. 931,430 and 931,303, both now abandoned, respectively. Likewise, the Merlin Express.RTM. is the subject matter of a design patent application filed under Ser. No. 931,631 on Nov. 17, 1986 issued 4/17/90 as patent D307,296. A font module for use in the Merlin Express.RTM. is the subject matter of U.S. patent application Ser. No. 119,810 filed Nov. 12, 1987, now abandoned.
The Merlin Express.RTM. employs a tape cassette (referred to as a cartridge in the aforementioned patent applications) which carries both an image receiving tape and an image carrying ribbon. The image receiving tape is carried on a spool housed in the cassette. The image carrying ribbon is likewise carried on a spool housed in the cassette. The image carrying tape is guided from its spool to a free end. A take-up spool is provided within the cassette for winding up the image carrying ribbon as it is utilized. The tape and ribbon are disposed so that in at least a predetermined location they are in face-to-face alignment. At the predetermined location, the cassette includes an opening which receives a transfer head and a platen when the cassette is mounted on the printing machine. The opposing tape and ribbon are disposed between the platen and the head. A gear mechanism within the head control apparatus urges the platen and head into close abutting relation with the tape and ribbon captured between them. Circuitry in the printing machine drives the platen to advance the tape and ribbon. When a desired character is inputted by an operator, the electronics of the machine energizes pixels on the thermal transfer head as the tape and ribbon advance past the head. When a command to print a letter is given a step motor actuates the platen. The head pixels are variously energized to imprint the letter on the tape.
In a printing machine such as the Merlin Express.RTM., the machine is limited in that only a particular width of tape can be used. Also, the amount of thermal energy which is needed to effect the transfer at the pixels preferably varies from one type of tape and pigment to another. For example, it may be desirable to transfer a white pigment onto a clear or black tape. Alternatively, it may be desirable to transfer a black pigment onto either a clear or a white tape. Due to variations in types of pigments and tapes, the optimum amount of energy to effect this transfer will vary with the types of tapes and ribbons being used. Likewise, it would be desirable for the machine to be able to sense numerous characteristics related to a cassette (size, density, type, etc.) by mere insertion of the cassette into the machine. However, heretofore, a printing machine was incapable of distinguishing such complex criteria without human intervention.